Is a gift legally mine if the other person is still paying for it?

My ex girlfriend is demanding i give her my laptop which she gave me as a Xmas present. If she doesn't get it back she says she will go to the police. She says she is still paying it off from the company she bought it from so legally she says it is hers as it's in her name. I have proof though that she gave it to me as an Xmas present. Can she legally take it back?